[U-Boot-Users] [PATCH V2] Round the serial port clock divisor value returned by calc_divisor()

[Wolfgang Denk]

In message <1215543298-26921-1-git-send-email-hugo.villeneuve at lyrtech.com> you wrote:
> Round the serial port clock divisor value returned by
> calc_divisor().
> 
> Signed-off-by: Hugo Villeneuve <hugo.villeneuve at lyrtech.com>
> Signed-off-by: John Roberts <john.roberts at pwav.com>
> 
> ---
> 
> Rounding is important, especially when using high baud rates
> values like 115200bps. When using the non-rounded value, some
> boards will work and some won't.
> 
>  drivers/serial/serial.c |    6 +++++-
>  1 files changed, 5 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/serial/serial.c b/drivers/serial/serial.c
> index 76425d8..1192f07 100644
> --- a/drivers/serial/serial.c
> +++ b/drivers/serial/serial.c
> @@ -144,8 +144,12 @@ static int calc_divisor (NS16550_t port)
>  #else
>  #define MODE_X_DIV 16
>  #endif
> -	return (CFG_NS16550_CLK / MODE_X_DIV / gd->baudrate);
>  
> +	/* Compute divisor value. Normally, we should simply return:
> +	 *   CFG_NS16550_CLK) / MODE_X_DIV / gd->baudrate
> +	 * but we need to round that value by adding 0.5 or 8/16.
> +	 * Rounding is especially important at high baud rates. */
> +	return (((16 * CFG_NS16550_CLK) / MODE_X_DIV / gd->baudrate) + 8) / 16;
>  }

Your patch causes problems with some boards:

Configuring for SBC8540 board...
serial.c: In function 'calc_divisor':
serial.c:153: warning: integer overflow in expression
serial.c:153: warning: integer overflow in expression

Configuring for sbc8548 board...
serial.c: In function 'calc_divisor':
serial.c:153: warning: integer overflow in expression
serial.c:153: warning: integer overflow in expression


Do you have a quick fix, or shall I back out the patch?

Best regards,

Wolfgang Denk

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